1. Field of the Invention
The present invention relates to communication control between communication nodes in asynchronous transfer mode (ATM) communication, and more particularly to an apparatus and a method for setting a communication path to prevent occurrence of congestion by detecting or monitoring traffic condition.
ATM is a specific packet oriented transfer mode using an asynchronous time division multiplexing technique. The multiplexed information flow is organized in fixed size blocks, called cells (ATM cell). An ATM cell consists of an information field and a header. The primary role of the header is to identify cells belonging to the same virtual path and virtual channel (VP/VC) connection. Cells are assigned on demand, depending on the source activity and the available resources. Cell sequence integrity on a virtual channel connection is preserved by the ATM Layer.
2. Description of the Prior Art
In recent years, B-ISDN (Broadband-Integrated Service Digital Network) has been emerging as the next generation public network, and with the deployment of the B-ISDN, even more flexible broadband communication networks than before are being realized which provide such differing services such as voice communications, very high speed file transfer, information communications, communications between LANs, moving images, and even moving image services of high-definition television (HDTV). ATM communication technology that can handle such multimedia is used in the B-ISDN.
In a B-ISDN network, a user terminal is connected to a communication node via a user network interface (UNI). Each communication node is connected to other communication nodes via node network interfaces (NNIs) and digital service units (DSUs) for high speed asynchronous transmission of ATM cells. Each communication node contains ATM adaptation layers (AALs) and ATM switches. The AALs perform ATM cell assembly and disassembly between the user terminals and the ATM switches. Data from each user terminal is broken up into a plurality of ATM cells by the AAL and a communication path is set up by the ATM switch.
Using the header data in each ATM cell, the ATM switch performs high speed switching operation by hardware. If communication path congestion is detected by the ATM switch during communication, the ATM switch discards part of the data transmitted from the transmitting user terminal. In this case, the ATM switch checks the CLP (cell loss priority) control bit in the ATM cell header and preferentially discards cells whose CLP value is "1".
For voice cells which generally have a high level of redundancy and are therefore less affected by cell discarding, the CLP is set to "1", whereas for other cells such as data, modem, facsimile data,etc., the CLP is set to "0".
As described above, since cell discarding occurs in ATM communication, it is necessary to have means for predicting abrupt occurrence of congestion by monitoring traffic information, and thereby, suitably exchanging a communication path.